This invention pertains to a process for the preparation of a shelf-stable self-crosslinking, one component aqueous urethane-vinyl polymer hybrid dispersions and to the shelf-stable, self-crosslinking dispersion itself.
Protective coatings for industrial application have been primarily solvent based using alkyd, polystyrene and nitrocellulose polymers. To meet the increasing environmental and safety concerns, the coatings industry is moving away from solvent-based systems towards water-based or high solids systems. Aqueous polyurethane hybrid dispersions have been developed for such applications. Patents describing aqueous polyurethane hybrid dispersions and their use, are as follows:
U.S. Pat. No. 4,644,030 discloses a method for making stable aqueous dispersions of polymeric material by producing an NCO-terminated polyurethane prepolymer in the presence of an inert liquid polymerizable monomer, dispersing the prepolymer in water, chain extending the prepolymer and then polymerizing vinyl monomer onto the polyurethane. The polyurethane prepolymer is prepared in conventional manner using a variety of available polyisocyanate, e g., aliphatic isocyanate, and reacting these isocyanate terminated polyurethanes with an active hydrogen-containing reactant, e.g., an hydroxyethylacrylate to form a polymerizable monomer and then dispersing this polymer in a monomer and an aqueous medium and effecting polymerization thereof. A water dispersing carboxyl providing reactant is incorporated into the polyurethane, such water-dispersing carboxyl reactant being an a,a-dimethylol C.sub.2-10 alkenoic acid, e.g., dimethylol propionic acid.
U.S. Pat. No. 3,684,758 discloses stable aqueous polymer dispersions which are formed by dispersing a polyurethane in vinyl monomer and then subjecting the vinyl monomer to radical polymerization in the aqueous medium in the presence of an emulsifier. A wide variety of monomers are suggested as being suited for polymerization in the presence of the polyurethane dispersed in the aqueous medium.
U.S. Pat. No. 3,759,873 discloses water dispersible polyurethane based polyesters prepared from carboxy polyols. The urethane modified unsaturated polyesters are then dissolved in a copolymerizable ethylenically unsaturated monomer and polymerized. These polyesters then can be blended with aminoplasts establishing a two-package system for effecting crosslinking at a later time. U.S. Pat. No. 5,225,460 discloses shelf stable emulsions based upon epoxy-based functional polymers and amino-containing hardeners. Shelf stability with crosslinking functionality is achieved through the use of a nonionic emulsifier, an emulsion polymerizable monomer having epoxy functional pendant groups and an emulsion polymerizable monomer having ethylenically unsaturated functionality.
U.S. Pat. No. 3,479,310 discloses improved polyurethane dispersions in water which are free from emulsifiers. The polyurethane dispersions contain from about 0.02 to about 1% of salt type groups, including quaternary nitrogen salts.
EPO 0 308 115 discloses surfactant free aqueous polymer dispersions containing an anionic water-dispersible polyurethane and a vinyl polymer.
U.S. Pat. No. 5,173,526 discloses a process for making stable aqueous urethane-acrylic polymer dispersions by subjecting vinyl monomers to radical emulsion polymerization in the presence of a high molecular weight polyurethane containing anionic groups.